FileMaker Apps for different clients

I have been playing around with the recent FM SDK to produce a few iPhone and IPad apps. The two options for distributing these seem to be either:

1. Get them accepted on the app store and make them available to anybody

or

2. Distribute them within a single 'enterprise' environment.

As a 'external' developer I have a number of different clients for whom I develop very different custom FM solutions. What I would like to do is distribute different apps to my different clients. It seems I might be able to do this using Apples Test Flight program but just wondered if there was any better way? I don't want to put the apps on the App store as they are not designed for 'general' use but only to make life easier for my clients and help them access their data remotely..